Effects of artificial sweeteners on metal bioconcentration and toxicity on a green algae Scenedesmus obliquus

The ecotoxicity of heavy metals depends much on their speciation, which is influenced by other coexisting substances having chelating capacity. In the present study, the toxic effects of Cd2+ and Cu2+ on a green algae Scenedesmus obliquus were examined in the presence of two artificial sweeteners (ASs), acesulfame (ACE) and sucralose (SUC) by comparing the cell specific growth rate mu and pulse-amplitude modulated (PAM) parameters (maximal photosystem II photochemical efficiency F-v/F-m, actual photochemical efficiency Yield, and non-photochemical quenching NPQ) of the algae over a 96-h period. Simultaneously, the bioconcentration of the metals by the algal cells in the presence of the ASs was measured. The presence of ACE enhanced the growth of S. obliquus and promoted the bioconcentration of Cd2+ in S. obliquus, while the impacts of SUC were not significant. Meanwhile, EC50 values of Cd2+ on the growth of S. obliquus increased from 0.42 mg/L to 0.54 mg/L and 0.48 mg/L with the addition of 1.0 mg/L ACE and SUC, respectively. As for Cu2+, EC50 values increased from 0.13 mg/L to 0.17 mg/L and 0.15 mg/L with the addition of 1.0 mg/L ACE and SUC, respectively. In summary, the two ASs reduced the toxicity of the metals on the algae, with ACE showing greater effect than SUC. Although not as sensitive as the cell specific growth rate, PAM parameters could disclose the mechanisms involved in metal toxicity at subcellular levels. This study provides the first evidence for the possible impact of ASs on the ecotoxicity of heavy metals. (C) 2016 Elsevier Ltd. All rights reserved.